DC offset correction of a power detector used with a continuous transmission radio frequency signal

ABSTRACT

The present invention relates to estimating a direct current (DC) offset of a power detection circuit when an estimated instantaneous amplitude of a continuous-transmission amplitude-modulated (AM) radio frequency (RF) signal is below a first threshold. The power detection circuit may be used to estimate an average output power associated with the continuous-transmission AM RF signal. The estimated average output power may be used as part of a feedback system to regulate the average output power. The estimated DC offset of the power detection circuit may be used to improve the estimate of the average output power, particularly over temperature and supply voltage variations. Estimating the DC offset of the power detection circuit when the estimated instantaneous amplitude of the continuous-transmission AM RF signal is below the first threshold may minimize errors in the estimated DC offset.

This application claims the benefit of provisional patent applicationSer. No. 60/916,890, filed May 9, 2007, the disclosure of which ishereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate to direct current (DC) powerdetectors, radio frequency (RF) transmitters, and RF receivers, whichmay be used in wireless communications systems.

BACKGROUND OF THE INVENTION

Direct current (DC) offsets often appear in electronic circuits thatprocess electrical signals. When the DC offsets are large enough, theymay interfere with proper processing of electrical signals.Additionally, changes in the DC offsets, such as changes that may occurover an operating temperature range or with power supply voltagevariations, may be problematic. One method to reduce the impact of DCoffsets is to interrupt processed electrical signals and then measureand compensate for DC offsets. However, in some circuits interruption ofprocessed electrical signals may not be possible. For example, in aradio frequency (RF) communications terminal, an RF transmitter maycontinuously transmit an RF transmit signal, such as in a single-carrierfrequency division multiple access (SC-FDMA) communications system orother fourth generation (4G) system, or as in a wideband code divisionmultiple access (WCDMA) communications system or other third generation(3G) system. It may not be possible to interrupt such an RF transmitsignal to make DC offset measurements of circuitry influenced by the RFtransmit signal.

Furthermore, an RF communications terminal may use a DC power detectorto measure the transmit power associated with a continuously transmittedRF signal. The DC power detector may have a DC offset that may affectmeasurements of the transmit power, particularly at low power levels. Ifthe continuously transmitted RF signal may not be interrupted so thatthe DC offset can be measured, another way to determine the DC offset isneeded. Similarly, the RF communications terminal may have an RFreceiver, which may have a DC offset and may be influenced by thecontinuously transmitted RF signal. If the continuously transmitted RFsignal may not be interrupted so that the DC offset of the RF receivercan be measured without the influence of the continuously transmitted RFsignal, another way to determine the DC offset is needed.

SUMMARY OF THE EMBODIMENTS

The present invention relates to estimating a direct current (DC) offsetof a power detection circuit when an estimated instantaneous amplitudeof a continuous-transmission amplitude-modulated (AM) radio frequency(RF) signal is below a first threshold. The power detection circuit maybe used to estimate an average output power associated with thecontinuous-transmission AM RF signal. The estimated average output powermay be used as part of a feedback system to regulate the average outputpower. The estimated DC offset of the power detection circuit may beused to improve the estimate of the average output power, particularlyover temperature and supply voltage variations. Estimating the DC offsetof the power detection circuit when the estimated instantaneousamplitude of the continuous-transmission AM RF signal is below the firstthreshold may minimize errors in the estimated DC offset.

In one embodiment of the present invention, a DC offset of an RFreceiver is estimated when the estimated amplitude of thecontinuous-transmission AM RF signal is below a second threshold andwhen the RF receiver is not receiving an RF input signal. The estimatedDC offset of the RF receiver may be used to improve RF receiverperformance, particularly over temperature and supply voltagevariations. Estimating the DC offset of the RF receiver when theestimated instantaneous amplitude of the continuous-transmission AM RFsignal is below the second threshold may minimize errors in theestimated DC offset. The continuous-transmission AM RF signal may beused in a single-carrier frequency division multiple access (SC-FDMA)communications system or other fourth generation (4G) system, or in awideband code division multiple access (WCDMA) communications system orother third generation (3G) system. The continuous-transmission AM RFsignal may be interrupted during slot boundaries between communicationsslots, such that a detector DC offset, a receiver DC offset, or both maybe estimated during the interruption.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 shows a radio frequency (RF) communications terminal applying acorrection for a receiver direct current (DC) offset to an RF inputsignal, according to a first embodiment of the present invention.

FIGS. 2A and 2B are graphs illustrating the relationships between anamplitude modulation signal, a continuous-transmissionamplitude-modulated (AM) RF signal, and an estimated amplitude signal ofthe RF communications terminal illustrated in FIG. 1.

FIG. 3 shows details of control circuitry illustrated in FIG. 1.

FIG. 4 shows the RF communications terminal applying a correction for adetector DC offset to a detected output power signal, according to asecond embodiment of the present invention.

FIGS. 5A, 5B, and 5C are graphs illustrating the relationships betweenthe amplitude modulation signal, the estimated amplitude signal, and adetected output power signal, respectively, of the RF communicationsterminal illustrated in FIG. 4.

FIGS. 6A and 6B are graphs illustrating the detected output power signalwith a positive detector DC offset and with a negative detector DCoffset, respectively, of the RF communications terminal illustrated inFIG. 4.

FIG. 7 shows details of the control circuitry illustrated in FIG. 4.

FIG. 8 shows the RF communications terminal applying a correction for areceiver DC offset to the RF input signal, and applying a correction fora detector DC offset to the detected output power signal, according to athird embodiment of the present invention.

FIG. 9 is a graph illustrating the estimated amplitude signal, such thata first threshold and a second threshold are unequal, according to oneembodiment of the RF communications terminal illustrated in FIG. 8.

FIG. 10 shows details of an RF receiver illustrated in FIG. 8.

FIG. 11 shows power detection circuitry of the RF communicationsterminal illustrated in FIG. 8 providing a temperature signal, accordingto one embodiment of the present invention.

FIG. 12 shows the power detection circuitry of the RF communicationsterminal illustrated in FIG. 8 providing a combined signal, according toan alternate embodiment of the present invention.

FIG. 13 shows details of the power detection circuitry illustrated inFIG. 12.

FIGS. 14A, 14B, and 14C illustrate the continuous-transmission AM RFsignal, an average output power of the continuous-transmission AM RFsignal, and the estimated amplitude signal of the RF communicationsterminal illustrated in FIG. 8, respectively, according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

In one embodiment of the present invention, a direct current (DC) offsetof a radio frequency (RF) receiver is estimated when an estimatedamplitude of a continuous-transmission amplitude-modulated (AM) RFsignal is below a first threshold and when the RF receiver is notreceiving an RF input signal. The estimated DC offset of the RF receivermay be used to improve RF receiver performance, particularly overtemperature and supply voltage variations. Estimating the DC offset ofthe RF receiver when the estimated instantaneous amplitude of thecontinuous-transmission AM RF signal is below the first threshold mayminimize errors in the estimated DC offset.

In an alternate embodiment of the present invention, a DC offset of apower detection circuit is estimated when the estimated instantaneousamplitude of the continuous-transmission AM RF signal is below a secondthreshold. The power detection circuit may be used to estimate anaverage output power associated with the continuous-transmission AM RFsignal. The estimated average output power may be used as part of afeedback system to regulate the average output power. The estimated DCoffset of the power detection circuit may be used to improve theestimate of the average output power, particularly over temperature andsupply voltage variations. Estimating the DC offset of the powerdetection circuit when the estimated instantaneous amplitude of thecontinuous-transmission AM RF signal is below the second threshold mayminimize errors in the estimated DC offset.

The continuous-transmission AM RF signal may be used in a single-carrierfrequency division multiple access (SC-FDMA) communications system orother fourth generation (4G) system, or in a wideband code divisionmultiple access (WCDMA) communications system or other third generation(3G) system. The continuous-transmission AM RF signal may be interruptedduring slot boundaries between communications slots, such that adetector DC offset, a receiver DC offset, or both may be estimatedduring the interruption. In another embodiment of the present invention,both the DC offset of the RF receiver and the DC offset of the powerdetection circuit are estimated when the estimated instantaneousamplitude of the continuous-transmission AM RF signal is below theappropriate thresholds.

FIG. 1 shows an RF communications terminal 10 applying a correction fora receiver DC offset to an RF input signal RF_(IN), according to a firstembodiment of the present invention. An RF transmitter 12 and an RFreceiver 14 are coupled to an antenna 16 through a duplexer 18. The RFtransmitter 12 feeds a continuous-transmission AM RF signal RF_(CTAM)through the duplexer 18 to the antenna 16, which transmits thecontinuous-transmission AM RF signal RF_(CTAM). The antenna 16 receivesand provides an RF input signal RF_(IN) to the RF receiver 14 throughthe duplexer 18. The RF receiver 14 may down convert the RF input signalRF_(IN) into a received signal V_(RX), which is fed to control circuitry20. The control circuitry 20 may further down convert, process, or both,the received signal V_(RX) into a received baseband signal BB_(RX),which is fed to a baseband controller 22. A transmit baseband signalBB_(TX) is fed from the baseband controller 22 to the RF transmitter 12,which uses the transmit baseband signal BB_(TX) to modulate an RFcarrier to provide the continuous-transmission AM RF signal RF_(CTAM).

The RF receiver 14 may have a receiver DC offset, which may introduce anoffset in the received signal V_(RX) when receiving the RF input signalRF_(IN); however, the DC offset may be estimated by measuring thereceived signal V_(RX) when the RF receiver 14 is not receiving the RFinput signal RF_(IN). Subsequently, the control circuitry 20 maysubtract the estimated DC offset from the received signal V_(RX) toimprove receiver performance. The receiver DC offset may be sensitive totemperature variations, supply voltage variations, or both. Therefore,the receiver DC offset may need to be estimated frequently.

The continuous-transmission AM RF signal RF_(CTAM) may be a continuouslytransmitted AM signal. In one embodiment of the present invention, thecontinuous-transmission AM RF signal RF_(CTAM) is a polar-modulated RFsignal, which may be a WCDMA transmit RF signal or other 3G transmitsignal. In another embodiment of the present invention, thecontinuous-transmission AM RF signal RF_(CTAM) is a polar-modulated RFsignal, which may be an SC-FDMA transmit RF signal or other 4G transmitsignal. The continuous-transmission AM RF signal RF_(CTAM) and the RFinput signal RF_(IN) may be associated with a full-duplex communicationsprotocol, such that the RF transmitter 12 and the RF receiver 14transmit and receive simultaneously. Therefore, to prevent interferencewith each other, the continuous-transmission AM RF signal RF_(CTAM) andthe RF input signal RF_(IN) may have different RF carrier frequencies.The duplexer 18 has a receive passband, which passes the RF input signalRF_(IN) from the antenna 16 to the RF receiver 14. Likewise, theduplexer 18 has a transmit passband, which passes thecontinuous-transmission AM RF signal RF_(CTAM) from the RF transmitter12 to the antenna 16.

Ideally, the duplexer 18 completely isolates the RF receiver 14 from thecontinuous-transmission AM RF signal RF_(CTAM); however, in practice,some of the continuous-transmission AM RF signal RF_(CTAM) may becoupled to the RF receiver 14 through the duplexer 18, through othercircuit paths, or both. The continuous-transmission AM RF signalRF_(CTAM) may interfere with estimates of the receiver DC offset and,since the continuous-transmission AM RF signal RF_(CTAM) is continuouslypresent, it may be desirable to estimate the receiver DC offset onlywhen the instantaneous amplitude of the continuous-transmission AM RFsignal RF_(CTAM) is below a first threshold V_(TH1). However, theinstantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM) may not be known directly. Therefore, in one embodiment of thepresent invention, estimates of the receiver DC offset are performedonly when an estimated instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) is below the firstthreshold V_(TH1). The control circuitry 20 uses the estimates of thereceiver DC offset to correct the received signal V_(RX).

The RF transmitter 12 may use an amplitude modulation signal V_(AM) toamplitude modulate an RF carrier to provide the continuous-transmissionAM RF signal RF_(CTAM). The amplitude modulation signal V_(AM) is fed tothe control circuitry 20 and may be used to estimate the instantaneousamplitude of the continuous-transmission AM RF signal RF_(CTAM). FIGS.2A and 2B are graphs illustrating the relationships between theamplitude modulation signal V_(AM), the continuous-transmission AM RFsignal RF_(CTAM), and an estimated amplitude signal V_(ESTAM) of the RFcommunications terminal 10 illustrated in FIG. 1. Since the amplitudemodulation signal V_(AM) is used to amplitude modulate an RF carrier toprovide the continuous-transmission AM RF signal RF_(CTAM), an RFenvelope V_(RFENV) tracks the amplitude of the continuous-transmissionAM RF signal RF_(CTAM). The positive side of the RF envelope V_(RFENV)defines an ideal estimated amplitude signal V_(ESTAM). When theestimated amplitude signal V_(ESTAM) is less than the first thresholdV_(TH1) and the RF receiver 14 is not receiving the RF input signalRF_(IN), the control circuitry 20 may estimate the receiver DC offset.

In one embodiment of the present invention, the estimated amplitudesignal V_(ESTAM) is continuously less than the first threshold V_(TH1);therefore, the control circuitry 20 may continuously estimate thereceiver DC offset. In another embodiment of the present invention, thecontrol circuitry 20 may estimate the receiver DC offset when thecontinuous-transmission AM RF signal RF_(CTAM) is disabled, such asbefore the continuous-transmission AM RF signal RF_(CTAM) is enabled,during slot boundaries between communications slots, or both. When theRF receiver 14 is not receiving the RF input signal RF_(IN), the RFreceiver 14 may receive other RF signals, such as noise or interferingsignals. To minimize the influence of the other RF signals on theestimate of the receiver DC offset, the control circuitry 20 mayestimate the receiver DC offset based on an average of the receivedsignal V_(RX).

FIG. 3 shows details of the control circuitry 20 illustrated in FIG. 1,according to one embodiment of the present invention. The amplitudemodulation signal V_(AM) is fed to amplitude estimating circuitry 24,which estimates the instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) to provide the estimatedamplitude signal V_(ESTAM). A first comparator 26 receives and comparesthe estimated amplitude signal V_(ESTAM) and the first thresholdV_(TH1). The first comparator 26 provides a receiver offset estimatingenable signal V_(ENROSE) to receiver DC offset estimating circuitry 28based on the comparison of the estimated amplitude signal V_(ESTAM) andthe first threshold V_(TH1).

When the estimated amplitude signal V_(ESTAM) is less than the firstthreshold V_(TH1), the receiver offset estimating enable signalV_(ENROSE) is in an enabled state, which enables estimating of thereceiver DC offset by the receiver DC offset estimating circuitry 28.When the estimated amplitude signal V_(ESTAM) is greater than the firstthreshold V_(TH1), the receiver offset estimating enable signalV_(ENROSE) is in a disabled state, which disables estimating of thereceiver DC offset by the receiver DC offset estimating circuitry 28.The receiver DC offset estimating circuitry 28 receives the receivedsignal V_(RX) and estimates the receiver DC offset when the RF receiver14 is not receiving the RF input signal RF_(IN) and the receiver offsetestimating enable signal V_(ENROSE) is in the enabled state based on thereceived signal V_(RX).

The receiver DC offset estimating circuitry 28 provides an estimated DCoffset ESTRXDCOS to receiver DC offset correction circuitry 30, whichreceives and applies a DC offset correction to the received signalV_(RX) to provide a corrected received signal V_(CRX) to correctedsignal down conversion circuitry 32. The receiver DC offset correctioncircuitry 30 may apply the DC offset correction by subtracting theestimated DC offset ESTRXDCOS from the received signal V_(RX). Thecorrected signal down conversion circuitry 32 further down converts thecorrected received signal V_(CRX) to provide the received basebandsignal BB_(RX). In an alternate embodiment of the present invention, thecorrected signal down conversion circuitry 32 is omitted and thecorrected received signal V_(CRX) directly provides the receivedbaseband signal BB_(RX).

FIG. 4 shows the RF communications terminal 10 applying a correction fora detector DC offset to a detected output power signal V_(DOP),according to a second embodiment of the present invention. The RFtransmitter 12 and the RF receiver 14 are coupled to the antenna 16through the duplexer 18. The RF transmitter 12 feeds thecontinuous-transmission AM RF signal RF_(CTAM) through the duplexer 18to the antenna 16, which transmits the continuous-transmission AM RFsignal RF_(CTAM). Power detection circuitry 34 is coupled between the RFtransmitter 12 and the duplexer 18, and detects the transmitted powerassociated with the continuous-transmission AM RF signal RF_(CTAM). Theantenna 16 receives and provides an RF input signal RF_(IN) to the RFreceiver 14 through the duplexer 18. The RF receiver 14 may down convertthe RF input signal RF_(IN) into the received baseband signal BB_(RX),which is fed to the baseband controller 22. The transmit baseband signalBB_(TX) is fed from the baseband controller 22 to the RF transmitter 12,which uses the transmit baseband signal BB_(TX) to modulate an RFcarrier to provide the continuous-transmission AM RF signal RF_(CTAM).

The power detection circuitry 34 provides the detected output powersignal V_(DOP) to the control circuitry 20 based on the detectedtransmitted power associated with the continuous-transmission AM RFsignal RF_(CTAM). The control circuitry 20 may estimate an averageoutput power associated with the continuous-transmission AM RF signalRF_(CTAM) based on the detected output power signal V_(DOP).Additionally, the control circuitry 20 may regulate the average outputpower associated with the continuous-transmission AM RF signal RF_(CTAM)based on the estimated average output power and a setpoint, such thatthe average output power is about equal to the setpoint. The controlcircuitry 20 may regulate the average output power by providing a powercontrol signal V_(PCONT) to the RF transmitter 12, which controls theamplitude of the continuous-transmission AM RF signal RF_(CTAM) based onthe power control signal V_(PCONT). The setpoint may be based on areceived command provided by the RF input signal RF_(IN).

The continuous-transmission AM RF signal RF_(CTAM) may be a continuouslytransmitted AM signal. In one embodiment of the present invention, thecontinuous-transmission AM RF signal RF_(CTAM) is a polar-modulated RFsignal, which may be a WCDMA transmit RF signal or other 3G transmitsignal. In another embodiment of the present invention, thecontinuous-transmission AM RF signal RF_(CTAM) is a polar-modulated RFsignal, which may be an SC-FDMA transmit RF signal or other 4G transmitsignal. The continuous-transmission AM RF signal RF_(CTAM) and the RFinput signal RF_(IN) may be associated with a full-duplex communicationsprotocol, such that the RF transmitter 12 and the RF receiver 14transmit and receive simultaneously. Therefore, to prevent interferencewith each other, the continuous-transmission AM RF signal RF_(CTAM) andthe RF input signal RF_(IN) may have different RF carrier frequencies.The duplexer 18 has a receive passband, which passes the RF input signalRF_(IN) from the antenna 16 to the RF receiver 14. Likewise, theduplexer 18 has a transmit passband, which passes thecontinuous-transmission AM RF signal RF_(CTAM) from the RF transmitter12 to the antenna 16.

The power detection circuitry 34 may have a detector DC offset, whichmay introduce an offset in the detected output power signal V_(DOP). Thedetector DC offset may be estimated by measuring the detected outputpower signal V_(DOP) when the continuous-transmission AM RF signalRF_(CTAM) is disabled. Subsequently, the control circuitry 20 maysubtract the estimated DC offset from the detected output power signalV_(DOP) to improve accuracy of the estimated average output power. Thedetector DC offset may be sensitive to temperature variations, supplyvoltage variations, or both. Therefore, the detector DC offset may needto be estimated frequently. Since the continuous-transmission AM RFsignal RF_(CTAM) is continuously present, it may not be possible todisable the continuous-transmission AM RF signal RF_(CTAM) to estimatethe detector DC offset. Therefore, according to one embodiment of thepresent invention, it may be desirable to estimate the detector DCoffset only when the instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) is below a secondthreshold V_(TH2).

The instantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM) may not be known directly. Therefore, in one embodiment of thepresent invention, estimates of the detector DC offset are performedonly when an estimated instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) is below the secondthreshold V_(TH2). The control circuitry 20 uses the estimates of thedetector DC offset to correct the detected output power signal V_(DOP).The RF transmitter 12 may use the amplitude modulation signal V_(AM) toamplitude modulate an RF carrier to provide the continuous-transmissionAM RF signal RF_(CTAM). The amplitude modulation signal V_(AM) is fed tothe control circuitry 20 and may be used to estimate the instantaneousamplitude of the continuous-transmission AM RF signal RF_(CTAM). Whenthe estimated amplitude signal V_(ESTAM) is less than the secondthreshold V_(TH2), the control circuitry 20 may estimate the detector DCoffset.

In one embodiment of the present invention, the control circuitry 20 mayestimate the receiver DC offset when the continuous-transmission AM RFsignal RF_(CTAM) is disabled, such as before the continuous-transmissionAM RF signal RF_(CTAM) is enabled, during slot boundaries betweencommunications slots, or both. To minimize the influence of noise orother signals on the estimate of the detector DC offset, the controlcircuitry 20 may estimate the detector DC offset based on an average ofthe detected output power signal V_(DOP). The detector DC offset may bevery sensitive to temperature changes. In an exemplary embodiment of thepresent invention, the detector DC offset may change between 20millivolts and 60 millivolts over an operating temperature range of theRF communications terminal 10. System requirements may restrict themaximum change of the detector DC offset to be less than one millivoltover the operating temperature range of the RF communications terminal10.

In one embodiment of the present invention, the RF communicationsterminal 10 includes temperature measurement and correction circuitry,which measures the temperature of the power detection circuitry 34 andprovides a temperature signal based on the measured temperature. Thetemperature measurement and correction circuitry temperature correctsthe detected output power signal V_(DOP) based on the temperaturesignal. Even with temperature correction, the detector DC offsettemperature drift in the detected output power signal V_(DOP) mayrequire further detector DC offset correction. In one embodiment of thepresent invention, the estimated detector DC offset tracks the actualdetector DC offset within one percent over the operating temperaturerange of the RF communications terminal 10.

FIGS. 5A, 5B, and 5C are graphs illustrating the relationships betweenthe amplitude modulation signal V_(AM), the estimated amplitude signalV_(ESTAM), and the detected output power signal V_(DOP), respectively,of the RF communications terminal 10 illustrated in FIG. 4. Since theamplitude modulation signal V_(AM) is used to amplitude modulate an RFcarrier to provide the continuous-transmission AM RF signal RF_(CTAM),the amplitude modulation signal V_(AM) may be used to estimate theinstantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM), and may produce the estimated amplitude signal V_(ESTAM).When the estimated amplitude signal V_(ESTAM) is less than the secondthreshold V_(TH2), the detected output power signal V_(DOP) is at aminimum; therefore, the control circuitry 20 may estimate the detectorDC offset based on the detected output power signal V_(DOP).

The estimated amplitude signal V_(ESTAM) is less than the secondthreshold V_(TH2) during an offset estimation period 36. During theoffset estimation period 36, the detected output power signal V_(DOP)may include effects of the detector DC offset and the detected power ofthe continuous-transmission AM RF signal RF_(CTAM). Since the controlcircuitry 20 may estimate the detector DC offset during the offsetestimation period 36, the detected power of the continuous-transmissionAM RF signal RF_(CTAM) represents an error in the estimation of thedetector DC offset. Therefore, according to one embodiment of thepresent invention, during the offset estimation period 36, the controlcircuitry 20 can estimate the instantaneous detected power of thecontinuous-transmission AM RF signal RF_(CTAM) based on the estimatedinstantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM) and subtract the estimated instantaneous detected power fromthe estimation of the detector DC offset. Thus, the estimated detectorDC offset is based on the detected output power signal V_(DOP) and theestimated instantaneous amplitude of the continuous-transmission AM RFsignal RF_(CTAM) during the offset estimation period 36.

According to an alternative embodiment of the present invention, duringthe offset estimation period 36, the control circuitry 20 can estimatethe average detected power of the continuous-transmission AM RF signalRF_(CTAM) based on an average estimated instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) during the offsetestimation period 36 and subtract the estimated average detected powerfrom the estimation of the detector DC offset. Thus, the estimateddetector DC offset is based on the detected output power signal V_(DOP)and the average estimated instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) during the offsetestimation period 36. In an additional embodiment of the presentinvention, the estimated instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) may be based on thedetected output power signal V_(DOP) instead of the amplitude modulationsignal V_(AM).

There may be a delay 37 between the amplitude modulation signal V_(AM)and the detected output power signal V_(DOP). Therefore, in oneembodiment of the present invention, the estimated instantaneousamplitude of the continuous-transmission AM RF signal RF_(CTAM) may bebased on the amplitude modulation signal V_(AM) and an estimate of thedelay 37 to improve accuracy in the estimation of the detector DCoffset. The power detection circuitry 34 may have a wide operating powerrange; however, estimation and error correction of the detector DCoffset may be more important at low average output power levels, such asbetween +5 decibel milliwatt (dbm) and −5 dbm. Therefore, in oneembodiment of the present invention, the second threshold V_(TH2) isbased on the estimated average output power.

FIGS. 6A and 6B are graphs illustrating the detected output power signalV_(DOP) with a positive detector DC offset V_(PDCO) and with a negativedetector DC offset V_(NDCO), respectively, of the RF communicationsterminal 10 illustrated in FIG. 4. A difference 38 between the detectedoutput power signal V_(DOP) and the positive detector DC offset V_(PDCO)or the negative detector DC offset V_(NDCO) is indicative of the truedetected power of the continuous-transmission AM RF signal RF_(CTAM).

FIG. 7 shows details of the control circuitry 20 illustrated in FIG. 4.The amplitude modulation signal V_(AM) is fed to the amplitudeestimating circuitry 24, which estimates the instantaneous amplitude ofthe continuous-transmission AM RF signal RF_(CTAM) to provide theestimated amplitude signal V_(ESTAM). A second comparator 40 receivesand compares the estimated amplitude signal V_(ESTAM) and the secondthreshold V_(TH2). The second comparator 40 provides a detector offsetestimating enable signal V_(ENDOSE) to detector DC offset estimatingcircuitry 42 based on the comparison of the estimated amplitude signalV_(ESTAM) and the second threshold V_(TH2).

When the estimated amplitude signal V_(ESTAM) is less than the secondthreshold V_(TH2), the detector offset estimating enable signalV_(ENDOSE) is in an enabled state, which enables estimating of thedetector DC offset by the detector DC offset estimating circuitry 42.When the estimated amplitude signal V_(ESTAM) is greater than the secondthreshold V_(TH2), the detector offset estimating enable signalV_(ENDOSE) is in a disabled state, which disables estimating of thedetector DC offset by the detector DC offset estimating circuitry 42.The detector DC offset estimating circuitry 42 receives the detectedoutput power signal V_(DOP) and estimates the detector DC offset whenthe detector offset estimating enable signal V_(ENDOSE) is in theenabled state based on the detected output power signal V_(DOP).

The detector DC offset estimating circuitry 42 provides an estimated DCoffset ESTDETDCOS to detector DC offset correction circuitry 44, whichreceives and applies a DC offset correction to the detected output powersignal V_(DOP) to provide a corrected detected output power signalV_(CDOP) to RF output power regulator circuitry 46. The detector DCoffset correction circuitry 44 may apply the DC offset correction bysubtracting the estimated DC offset ESTDETDCOS from the detected outputpower signal V_(DOP). The RF output power regulator circuitry 46 mayestimate the average output power associated with thecontinuous-transmission AM RF signal RF_(CTAM) based on the correcteddetected output power signal V_(CDOP). Additionally, the RF output powerregulator circuitry 46 may regulate the average output power associatedwith the continuous-transmission AM RF signal RF_(CTAM) based on theestimated average output power and a power setpoint P_(SP), such thatthe average output power is about equal to the power setpoint P_(SP).The RF output power regulator circuitry 46 may regulate the averageoutput power by providing the power control signal V_(PCONT) to the RFtransmitter 12, which controls the amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) based on the powercontrol signal V_(PCONT).

FIG. 8 shows the RF communications terminal 10 applying a correction fora receiver DC offset to the RF input signal RF_(IN), and applying acorrection for a detector DC offset to the detected output power signalV_(DOP), according to a third embodiment of the present invention. Anyor all of the embodiments of the present invention associated with theRF communications terminal 10 illustrated in FIG. 1 may be combined withany or all of the embodiments of the present invention associated withthe RF communications terminal 10 illustrated in FIG. 4.

FIG. 9 is a graph illustrating the estimated amplitude signal V_(ESTAM),such that the first threshold V_(TH1) and the second threshold V_(TH2)are unequal, according to one embodiment of the RF communicationsterminal 10 illustrated in FIG. 8. The instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) that is significantrelative to the receiver DC offset may be different from theinstantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM) that is significant relative to the detector DC offset.Therefore, the first and second thresholds V_(TH1), V_(TH2) may beunequal. In an alternate embodiment of the present invention, theinstantaneous amplitude of the continuous-transmission AM RF signalRF_(CTAM) that is significant relative to the receiver DC offset may beabout equal to the instantaneous amplitude of thecontinuous-transmission AM RF signal RF_(CTAM) that is significantrelative to the detector DC offset. Therefore, the first and secondthresholds V_(TH1), V_(TH2) may be about equal.

FIG. 10 shows details of the RF receiver 14 illustrated in FIG. 8,according to one embodiment of the present invention. The RF inputsignal RF_(IN) feeds down conversion circuitry 48, which down convertsthe RF input signal RF_(IN) into a down converted signal V_(DCV), whichis an analog signal. The down converted signal V_(DCV) feeds a firstanalog-to-digital converter 50, which converts the analog down convertedsignal V_(DCV) into the received signal V_(RX), which is a digitalsignal. In alternate embodiments of the present invention, the downconversion circuitry 48, the first analog-to-digital converter 50, orboth may be omitted.

FIG. 11 shows the power detection circuitry 34 of the RF communicationsterminal 10 illustrated in FIG. 8 providing a temperature signalV_(TEMP) to the control circuitry 20, according to one embodiment of thepresent invention. The temperature signal V_(TEMP) is based on thetemperature of the power detection circuitry 34. The control circuitry20 may estimate the detector DC offset to create an estimatedtemperature based detector DC offset based on the temperature signalV_(TEMP). The estimated temperature based detector DC offset may bebased on previously collected data relating the detector DC offset tothe temperature of the power detection circuitry 34. The controlcircuitry 20 may then estimate the detector DC offset based on both thedetected output power signal V_(DOP) and the temperature signalV_(TEMP).

FIG. 12 shows the power detection circuitry 34 of the RF communicationsterminal 10 illustrated in FIG. 8 providing a combined signal V_(COMB)to the control circuitry 20, according to an alternate embodiment of thepresent invention. The control circuitry 20 provides a select signalV_(SEL) to the power detection circuitry 34. The combined signalV_(COMB) may be based on either the detected output power signal V_(DOP)(not shown) or the temperature signal V_(TEMP) (not shown), depending onthe select signal V_(SEL).

FIG. 13 shows details of the power detection circuitry 34 illustrated inFIG. 12, according to one embodiment of the present invention. An RFcoupler 52 is coupled between the RF transmitter 12 and the duplexer 18,and provides a coupled signal V_(CPL) to an RF power detector 54 basedon the continuous-transmission AM RF signal RF_(CTAM). The RF powerdetector 54 detects the transmitted power associated with thecontinuous-transmission AM RF signal RF_(CTAM) based on the coupledsignal V_(CPL). The RF power detector 54 provides an analog detectedoutput power signal V_(ADOP) to a multiplexer 56 based on the detectedtransmitted power.

Temperature measurement circuitry 58 provides an analog temperaturesignal V_(ATEMP) to the multiplexer 56. The analog temperature signalV_(ATEMP) is based on the temperature of the power detection circuitry34. The multiplexer 56 provides a multiplexer output signal V_(MUXO)based on either the analog detected output power signal V_(ADOP) or theanalog temperature signal V_(ATEMP), depending on the select signalV_(SEL). A second analog-to-digital converter 60 converts themultiplexer output signal V_(MUXO) into the combined signal V_(COMB),which is a digital signal. In alternate embodiments of the presentinvention, the second analog-to-digital converter 60 may be omitted.

FIGS. 14A, 14B, and 14C illustrate the continuous-transmission AM RFsignal RF_(CTAM), an average output power P_(AO) of thecontinuous-transmission AM RF signal RF_(CTAM), and the estimatedamplitude signal V_(ESTAM) of the RF communications terminal 10illustrated in FIG. 8, respectively, according to one embodiment of thepresent invention. Some communications protocols continuously transmitsequential communications slots, one after the other. Adjacentcommunications slots may be separated in time by slot boundaries. Forexample, the continuous-transmission AM RF signal RF_(CTAM) may transmitan Nth slot 62, followed by a slot boundary 64 having a slot duration66, which may be followed by an N+1st slot 68. During the slot boundary64, the continuous-transmission AM RF signal RF_(CTAM) may beinterrupted during an interrupt event 70 to allow estimation of thedetector DC offset, the receiver DC offset, or both, as illustrated inFIG. 14A.

The time duration of the interrupt event 70 is an interrupt duration 72,as illustrated in FIG. 14B. During the interrupt event 70, the averageoutput power P_(AO) may ramp down from a first power level P₁ to aboutzero, may be held at zero for a zero power duration 74 to allow time forestimation of the detector DC offset and to allow time for determinationof a second power level P₂ based on the estimated detector DC offset,and may ramp up from about zero to the second power level P₂. The timeduration of the ramp down is a ramp down duration 76 and the timeduration of the ramp up is a ramp up duration 78.

In a first exemplary embodiment of the present invention, the slotduration 66 may be about 25 microseconds and the interrupt duration 72may be less than about eight microseconds. In a second exemplaryembodiment of the present invention, the slot duration 66 may be about25 microseconds, the interrupt duration 72 may be about sixmicroseconds, the zero power duration 74 may be about four microseconds,the ramp down duration 76 may be about one microsecond, and the ramp upduration 78 may be about one microsecond. During the zero power duration74, the first and second thresholds are V_(TH1), V_(TH2) are greaterthan the estimated amplitude signal V_(ESTAM), which may meet some orall of the criteria needed to enable estimation of the detector DCoffset, the receiver DC offset, or both, as illustrated in FIG. 14C.

Some of the circuitry previously described may use discrete circuitry,integrated circuitry, programmable circuitry, non-volatile circuitry,volatile circuitry, software executing instructions on computinghardware, firmware executing instructions on computing hardware, thelike, or any combination thereof. The computing hardware may includemainframes, micro-processors, micro-controllers, digital signalprocessors (DSPs), the like, or any combination thereof.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present invention. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

1. A radio frequency (RF) communications terminal comprising: an RFtransmitter adapted to transmit a continuous-transmissionamplitude-modulated (AM) RF signal at an average output power; a powerdetection circuit adapted to provide a detected output power signalbased on an amplitude of the continuous-transmission AM RF signal and afirst detector direct current (DC) offset of the power detectioncircuit; and control circuitry adapted to: estimate the first detectorDC offset based on the detected output power signal when an estimatedinstantaneous amplitude of the continuous-transmission AM RF signal isless than a first threshold; estimate the average output power based onthe detected output power signal and the estimated first detector DCoffset; and regulate the average output power based on the estimatedaverage output power and a first setpoint.
 2. The RF communicationsterminal of claim 1 wherein the continuous-transmission AM RF signal isa polar-modulated RF signal.
 3. The RF communications terminal of claim1 wherein the continuous-transmission AM RF signal is a wideband codedivision multiple access (WCDMA) transmit RF signal.
 4. The RFcommunications terminal of claim 1 wherein the continuous-transmissionAM RF signal is a single-carrier frequency division multiple access(SC-FDMA) transmit RF signal.
 5. The RF communications terminal of claim1: further comprising temperature measurement circuitry adapted toprovide a temperature signal based on a temperature of the powerdetection circuit; and wherein the estimated first detector DC offset isfurther based on the temperature signal.
 6. The RF communicationsterminal of claim 1: further comprising temperature measurement andcorrection circuitry adapted to provide a temperature signal based on atemperature of the power detection circuit; and wherein the detectedoutput power signal is further based on the temperature signal.
 7. TheRF communications terminal of claim 1 wherein the estimatedinstantaneous amplitude of the continuous-transmission AM RF signal isbased on the detected output power signal.
 8. The RF communicationsterminal of claim 1 wherein: the control circuitry is further adapted toprovide an amplitude modulation signal; and the continuous-transmissionAM RF signal is based on the amplitude modulation signal.
 9. The RFcommunications terminal of claim 8 wherein the estimated instantaneousamplitude of the continuous-transmission AM RF signal is based on theamplitude modulation signal.
 10. The RF communications terminal of claim9 wherein the estimated instantaneous amplitude of thecontinuous-transmission AM RF signal is further based on an estimateddelay between the amplitude modulation signal and the detected outputpower signal.
 11. The RF communications terminal of claim 9 wherein theestimated first detector DC offset is further based on the estimatedinstantaneous amplitude of the continuous-transmission AM RF signal whenthe estimated instantaneous amplitude of the continuous-transmission AMRF signal is less than the first threshold.
 12. The RF communicationsterminal of claim 11 wherein the estimated first detector DC offset isfurther based on an average of the estimated instantaneous amplitude ofthe continuous-transmission AM RF signal when the estimatedinstantaneous amplitude of the continuous-transmission AM RF signal isless than the first threshold.
 13. The RF communications terminal ofclaim 11: further comprising temperature measurement circuitry adaptedto provide a temperature signal based on a temperature of the powerdetection circuit; and wherein the estimated first detector DC offset isfurther based on the temperature signal.
 14. The RF communicationsterminal of claim 13 wherein: the control circuitry is further adaptedto estimate a second detector DC offset of the power detection circuitwhen the continuous-transmission AM RF signal is disabled; and theestimated first detector DC offset is further based on the estimatedsecond detector DC offset.
 15. The RF communications terminal of claim 1wherein: the control circuitry is further adapted to estimate a seconddetector DC offset of the power detection circuit when thecontinuous-transmission AM RF signal is disabled; and the estimatedfirst detector DC offset is further based on the estimated seconddetector DC offset.
 16. The RF communications terminal of claim 1wherein the first threshold is based on the estimated average outputpower.
 17. The RF communications terminal of claim 1 wherein: the RFtransmitter is further adapted to interrupt the continuous-transmissionAM RF signal during slot boundaries between communications slots; andthe control circuitry is further adapted to estimate the first detectorDC offset of the power detection circuit during the interruption of thecontinuous-transmission AM RF signal.
 18. The RF communications terminalof claim 17 wherein a duration of the interruption of thecontinuous-transmission AM RF signal is less than about eightmicroseconds.
 19. The RF communications terminal of claim 1 wherein:temperature changes of the power detection circuit produce first changesof the estimated first detector DC offset and second changes of thefirst detector DC offset; and absolute values of the first changes areless than about one percent of absolute values of the second changes.20. The RF communications terminal of claim 19 wherein absolute valuesof the first changes are less than about one millivolt.
 21. The RFcommunications terminal of claim 1 further comprising an RF receiveradapted to receive an RF input signal and provide a received signalbased on the RF input signal and a first receiver DC offset of the RFreceiver, and the control circuitry is further adapted to: estimate thefirst receiver DC offset based on the received signal when: the RFreceiver is not receiving the RF input signal; and the estimatedinstantaneous amplitude of the continuous-transmission AM RF signal isless than a second threshold; and provide a corrected received signalbased on the received signal and the estimated first receiver DC offset.22. The RF communications terminal of claim 21 wherein: the controlcircuitry is further adapted to estimate a second receiver DC offset ofthe RF receiver when the continuous-transmission AM RF signal isdisabled; and the estimated first receiver DC offset is further based onthe estimated second receiver DC offset.
 23. The RF communicationsterminal of claim 21 wherein: the RF transmitter is further adapted tointerrupt the continuous-transmission AM RF signal during slotboundaries between communications slots; and the control circuitry isfurther adapted to estimate the first receiver DC offset during theinterruption of the continuous-transmission AM RF signal.
 24. The RFcommunications terminal of claim 21 further comprising a duplexercoupled between the RF transmitter and the RF receiver.
 25. A method foroperating a radio frequency (RF) communications terminal comprising:transmitting a continuous-transmission amplitude-modulated (AM) RFsignal at an average output power; providing a power detection circuithaving a first detector direct current (DC) offset; providing a detectedoutput power signal based on an amplitude of the continuous-transmissionAM RF signal and the first detector DC offset; estimating the firstdetector DC offset based on the detected output power signal when anestimated instantaneous amplitude of the continuous-transmission AM RFsignal is less than a first threshold; estimating the average outputpower based on the detected output power signal and the estimated firstdetector DC offset; and regulating the average output power based on theestimated average output power and a first setpoint.